Study on the molecular mechanism of grass carp's adaptation to eutrophication

In recent years, freshwater fisheries have witnessed rapid development. However, the intensive and high-density aquaculture technology has led to severe eutrophication of aquaculture water, which has become one of the main factors hindering the sustainable development of the fish aquaculture industry. Grass carp, a common herbivorous fish characterized by rapid growth and strong adaptability, plays a significant role in aquaculture. To explore the mechanism of grass carp adaptation to the eutrophic environment, this study conducted a 30-day culture experiment using mildly eutrophic water as the preliminary culture environment, with common grass carp and gynogenetic disease-resistant grass carp being cultured in the eutrophic environment. By employing techniques such as transmission electron microscopy, histological paraffin sections, blood smears, real-time fluorescence quantitative PCR , and the measurement of antioxidant enzyme activity, it was dound that eutrophic conditions cause damage to various tissues and organs of grass carp. The antioxidant system's beneficial response to environmental stress and immune activation were also observed. Moreover, disease-resistant grass carp exhibited greater adaptability and effectiveness in regulating inflammation compared to normal grass carp. When combined with transcriptome analysis, it was revealed that the fish withstand this unfavorable environment by enhancing their metabolism and activating the immune pathway. As a result, it was discovered that peroxisome proliferator-activated receptor (PPAR) and vascular endothelial growth factor(VEGF) signaling pathways may work in concert to help grass carp adapt to their eutrophic surroundings. This study provides a molecular basis for a comprehensive investigation of fish's environmental adaptation mechanism, which is extremely valuable for the selection and breeding of resilient species as well as the healthy culture of freshwater fish.